Insects have evolved resistance to many of the poisons we've used to kill them …

The indiscriminate spraying of pesticides has probably caused as many problems as it has solved, but here's one that was not expected: some bacteria have decided that one insecticide is a very tasty meal. Unfortunately for us, one of the strains of bacteria that has evolved the ability to digest the toxin happens to be able to find a home in an insect's gut. When it does so, it provides the insect with resistance.

Several factors had to come together for this to take place, but one was the heavy use of fenitrothion, which is described as "one of the most popular organophosphorus insecticides used worldwide" by the authors of a study of these insects. It has apparently been so widely deployed that a variety of bacteria have evolved the ability to use it as a food source. Most of these simply inhabit the soil in the fields where it is used and, at worst, cut down on the level of insecticide present and thereby make life a bit easier for the insects.

One of the bacterial species, Burkholderia has a rather unusual ability. Not only can the strain make a living in the soil, but it can also take up residence inside the gut of insects, acting as what's called a "endosymbiont." In most cases, insects transfer endosymbionts as contaminants on the egg, which take up residence in the offspring as they hatch—these bacteria never have to spend any time living outside an insect. Burkholderia, then, is rather unusual, in that the bugs seem to pick up an infection from the environment. It's still a symbiont, though, as animals that carry these bacteria tend to live longer and grow larger than their peers that don't have any in their guts.

The researchers describe a series of fairly straightforward experiments that make their case. When they took a pot of soil and treated it weekly with fenitrothion, they found that it actually boosted the bacterial population, and that 80 percent of the bacteria that grew out were able to digest the toxin. (Conveniently, an intermediate in the digestion process is yellow, while the original compound is completely colorless.) This confirmed that the pesticide could be a useful food source.

They then grew plants in both sets of soil, and added eggs from an agricultural pest called the bean bug (Riportus pedestris in formal situations). Those bean bugs that were grown on insecticide-treated soil ended up with bacteria in their midgut that could digest the pesticide. Surprisingly, this not only provided protection when the insects ingested fenitrothion, but it protected them from surface exposure as well.

Is this a problem out in the fields? Their first scan of insects from agricultural areas came up empty. But the authors noted that the Japanese agricultural system (they were based in Japan) doesn't tend to use heavy doses or repeated spraying of these insecticides, suggesting there wasn't sufficient selective pressure for either the bacteria or the insects to partner with them. So, they specifically looked for areas where fenitrothion has been used extensively, finding it on a remote subtropical island far from the main islands of Japan. The bacteria isolated from the sugarcane fields there could digest the pesticide, and the insects that carried them showed high levels of resistance to it.

We've already known from countless examples that repeated, heavy use of a single pesticide (or drug) can help select for the evolution of resistant organisms. But generally, this selection is thought to occur over multiple generations which, for insects, tends to take a fair bit of time. Bacteria, however, can go through several generations in a day, and a single source of Burkholderia can presumably be transferred to many insects within a population.

The good news here is that, where fenitrothion is used sparingly, this resistance doesn't seem to be a problem. If the bacteria can't guarantee it will be there to provide a meal, they won't evolve or maintain the genes needed to digest it.

@dirkvs I'm sure we could. However, in this case the bacteria that live in the insects' guts need the pesticide to live. So while we could engineer (genetically or otherwise) bacteria for our guts that can digest cyanide for us we'd then have to make sure to consume enough cyanide in our daily routine to keep the bugs healthy.

This is why biodiversity is so important. Moving towards a handful of genetically modified "super crops" creates a monoculture that is just one disaster away decimating our food supply. All it takes is one incredibly resilient pestilence to build a resistance to the GMO defenses and herbicides. Then, we don't have anything to replace it. Better to create a wide variety of every type of crop (e.g. corn, potatoes, rice, wheat, etc.) so that at least a few varieties would be resilient to pestilence and others to fall back on in a case of disaster.

This doesn't just apply to genetically modified things. This can happen with any type of pesticide system. There are fixes for this its even mentioned in the article. This does have an effect on the way GMs are deployed. Because GMs will guarantee the existence of said pesticide if it is produced by the plant or if it s designed for an immunity to said pesticide because it will be dumped.I believe that farmers should have to buy mixed seeds. They seem to be lazy about implementing proper techniques(checkerboarding) to prevent this type of thing. I guess its to be expected its about maximizing profits even though it puts them at risk for a wipeout.

This is why biodiversity is so important. Moving towards a handful of genetically modified "super crops" creates a monoculture that is just one disaster away decimating our food supply. All it takes is one incredibly resilient pestilence to build a resistance to the GMO defenses and herbicides. Then, we don't have anything to replace it. Better to create a wide variety of every type of crop (e.g. corn, potatoes, rice, wheat, etc.) so that at least a few varieties would be resilient to pestilence and others to fall back on in a case of disaster.

Very true. This isn't a case of being cautious -- the Irish potato famine and the 1970 corn blight in the US were both caused by monocropping with a single variety when there were resistant genes available in other varieties. The corn land races, in particular, are incredibly important to maintain given the worldwide reliance on corn, but more of those land races are being lost every year.

Just because it's a 'popular insecticide', doesn't mean it has anything to do with food. This and the last similar article concern insecticides mostly used in cities. Why are people so quick to jump on farmers when it's actually there own frivilous and uncontrolled use that's more the problem. Same with the ridiculously huge use of fertilizers on lawns.

This is why it's very important to hit as many different modes of action as possible and rotate insecticides. There's even a group dedicated to avoiding these very problems, IRAC I believe. Not like the iRack, of course.

Though this new mode of action is something to watch out for, it's important to realize any mutation in a bacteria that allows it to consume these pesticides has to be beneficial relative to the current population, otherwise they'll be crowded out. That may be why we haven't seen this mode of resistance before; it's rare.